The invention relates to a TEM FIB sample as well as to a method for the production of such a sample.
Samples for transmission electron microscopy (TEM) can be prepared in different ways. To be able to observe samples with a TEM, these must be thinned correspondingly defined such that they can be transmitted by electrons in the TEM. The quality of the image resolution is substantially dependent on the quality of the sample. For this purpose the sample must be uniformly set to a correspondingly desired defined thickness in a corresponding etching process. It is here important that in this etching process the sample structure is not altered by the process itself. However, this does not yield the desired quality of the sample appropriate to current requirements. The wet-chemical etching method does not lead to the desired goal.
For this reason, for high-quality TEM samples the samples are today worked by etching with a fixed argon ion beam having, for example, a diameter of approximately 1 mm. A further known method, and one preferred today, comprises cutting out the sample with a focused ion beam (FIB technique) and to thin it as desired. Herein a finely focused scanning gallium ion beam with a beam diameter of a few nm is employed, with the aid of which TEM samples can be prepared from the solid material in the form of lamellae by perpendicular bombardment of the surface. Typically the sample lamellae are herein approximately 80 to 100 nm thick. This latest FIB preparation technique is described for example in P. Gnauck, P. Hoffrogge, ICEM 15, Durban, (Suppl. 1: Proceedings), (2002) 3, 32.
The technique for producing FIB samples for TEM lamellae does, however, have various disadvantages. The lamella cannot be prepared of sufficient thinness for the samples to be well suited for high-resolution transmission electron microscopy (HRTEM). The TEM lamella is moreover contaminated through the preparation and, in comparison to conventional ion beam preparation with fixed ion beam, has significantly greater margin amorphization. This margin amorphization is a disturbance of the original structure in the surface of the sample and specifically on both sides of the sample and this occurs to a depth of approximately 20 nm on both sides of the sample. In conventional sample production by means of fixed ion beam etching, this destruction of the original structure extends only to a depth of approximately 5 nm. However, the advantages, such as for example the target precision of the scanning FIB technique cannot be attained.
The above listed problems lead to a strongly reduced sample quality. To be able to solve these problems, attempts have recently been made to subsequently thin the FIB samples with the aid of conventional non-scanning ion beam preparation. But, due to the sample geometry and the etching on one side of the lamella, additional undesirable contamination occurs. Such contaminations negate the advantage of the subsequent treatment and make the sample unusable. The problematic issue in subsequent working of FIB samples is described in prior art in Max V. Siderov, Microsc. Microanal. 8 (Suppl. 2: Proceedings), (2002) 560 CD.
The invention addresses the problem of eliminating the disadvantages of prior art, but in particular of realizing TEM samples, which make possible a high quality, but in particular a high resolution and detail reproduction when observing with the TEM.